Cylindrical cover-attached encoder apparatus

ABSTRACT

A cylindrical cover-attached encoder apparatus, including a magnetic metal-based body having a cylindrical shape, a magnetic rubber-based encoder having a cylindrical shape and formed around the outer peripheral surface of said magnetic metal-based cylindrical body, and a nonmagnetic material-based cover having a cylindrical shape and adapted to be mounted on said magnetic rubber-based encoder for covering the outer peripheral surface of the cylindrical portion of said magnetic rubber-based encoder.

This application is a continuation of U.S. application Ser. No.11/439,992, filed May 25, 2006, which is a continuation of U.S.application Ser. No. 10/959,084, filed Oct. 7, 2004, now abandoned.

BACKGROUND

1. Field of the Invention

The present invention relates to an encoder apparatus, or morespecifically an encoder that is included in the encoder apparatus as oneof its components, wherein the encoder apparatus may be mounted on arotational member in the automotive vehicle (such as between the outerand inner races of the wheel bearing unit on the driving shaft or drivenshaft) for detecting the number of revolutions of the rotational member.

2. Description of the Prior Art

One example of the conventional encoder apparatus that may be mounted ona rotational member in the automotive vehicle by pressing the encoderapparatus into the rotational member for detecting the number ofrevolutions of the rotational member is disclosed in Japanese patentapplication as now published under No. 62(1987)-25267, for example,wherein the encoder apparatus includes an encoder in the form of amagnetic signal generator ring.

As described in the above document, the magnetic signal generator ringis based on a synthetic resin material that is mechanically strongenough to avoid any possible damages that might occur on the ring as itis pressed into the rotational member, and includes an annular syntheticresin magnet that is buried around the outer peripheral surface of thering. The synthetic resin magnet takes the form of a multipole magnethaving S polarities and N polarities magnetized alternately at equalintervals in the circumferential direction.

As the encoder apparatus is mounted on the rotational member in themanner described above, the encoder in the encoder apparatus may beplaced to face opposite the sensor that is located adjacently to theencoder outside it.

As the rotational member on which the encoder apparatus is mounted isthus rotating at the number of revolutions that is changing everymoment, the encoder may magnetically produce pulses each of whichrepresent the respective ever-changing number of revolutions and thesensor may detect the ever-changing number of revolutions by respondingto each of the pulses.

In the conventional encoder apparatus described above, however, there isa risk that some extraneous matter such as stones might enter the areabetween the encoder in the encoder apparatus and the sensor located toface opposite the encoder outside it. So that, said extraneous mattersuch as stones might be engaged between the encoder and the sensor, andthus it causing damages on the encoder.

The side of the encoder facing opposite the sensor is magnetized asdescribed above, acting as the magnetized surface having alternate Npolarities and S polarities appear at equal intervals. If thismagnetized surface may be damaged by the extraneous matter such asstones which entering the area between the encoder and sensor, thesensor would not be able to detect the number of revolutions correctlybecause the encoder would fail to function properly. Thus, this presentsa serious disadvantage.

Another example of the conventional encoder apparatus that includes anencoder known as the annular encoder is disclosed in Japanese patentapplication as now published under No. 2001-241435, wherein the encoderapparatus may be mounted on a rotational member, such as between theinner and outer races of the bearing unit rotating relative to eachother, so that it can detect the number of revolutions. In thisconventional encoder apparatus, the encoder is covered by a nonmagneticcover on the side thereof facing opposite the sensor in order to avoidthat the damages might occur on the encoder as described above. Otherexamples of the encoder apparatus are disclosed in Japanese patentapplications as now published under No. H5 (1993)-249126, No. H11(1999)-303879, and No. 2002-286739, respectively.

For those recent years, the encoder apparatus that may be mounted on arotational member on the automotive vehicle by pressing the encoderapparatus into the rotational member for detecting the ever-changingnumber of revolutions for the rotational member has more often been usedwith the FF (front engine, front drive) vehicle in particular, in whichthe encoder apparatus is mounted on the drive shaft and the like, and isused under the more severe running or ambient conditions.

SUMMARY OF THE INVENTION

In order to avoid that any damages occur on the encoder in the encoderapparatus when it is mounted on the rotational member by pressing itinto the rotational member, there are demands for the encoder apparatusthat includes an encoder that is mechanically strong enough to permitthe encoder to withstand any severe or vigorous ambient or runningconditions, thereby protecting the encoder from such damages moresecurely.

In order to solve the problems associated with the prior art encoderapparatus as described above, the present invention proposes to providea cylindrical cover-attached encoder apparatus that includes a magneticmetal-based body having the cylindrical shape, a magnetic rubber-basedencoder having the cylindrical shape and formed around the cylindricalportion of the magnetic metal-based cylindrical body, and a nonmagneticmaterial-based cover having the cylindrical shape and mounted on themagnetic rubber-based encoder for covering the outer peripheral surfaceof the cylindrical portion of the encoder.

It may be understood that as the cylindrical cover-attached encoderapparatus according to the present invention includes the magneticrubber-based cylindrical encoder that may be formed around thecylindrical portion of the magnetic metal-based cylindrical body, it canhave the improved mechanical strength that enables the encoder apparatusto be mounted on the rotational member without causing any damages onthe encoder in the encoder apparatus when the encoder apparatus ispressed into the rotational member.

It may also be understood that as the magnetic rubber-based cylindricalencoder has its outer peripheral side covered by the nonmagneticmaterial-based cover, it can be protected from any unfavorable ambientconditions outside it, and it can withstand any severe or vigorousrunning or ambient conditions for an extended period of the time withoutcausing any damages, even when it is used under such conditions.

The cylindrical encoder that constitutes one component of thecylindrical cover-attached encoder apparatus according to the presentinvention may be any type of the encoder that is known to any personskilled in the relevant art. For example, the cylindrical encoder may beformed by preparing ferrite magnetic powders (such as strontium ferritepowder, barium ferrite powder and the like) or rare earth magneticpowders (such as a combination of neodymium, iron and boron, acombination of samarium, iron and nitrogen and the like), adding any ofthe above powders to elastic element such as synthetic rubber orsynthetic resin, mixing them together, and molding the mixture into thecylindrical shape by using the vulcanizing, molding process. Then, saidmolded cylindrical shape may be magnetized so that S polarities and Npolarities can appear alternately at equal intervals in thecircumferential direction thereof Finally, the multipole encoder havingthe cylindrical shape can be obtained. This cylindrical encoder may thenbe attached to the magnetic metal-based cylindrical body by using anyadhesive medium.

It should be noted that the ferrite magnetic powder or rare earthmagnetic powder and the elastic element such as synthetic rubber orsynthetic resin may preferably have the composition ratio range ofbetween 70% and 95% by weight.

The synthetic rubber that may be based on the encoder may include NBR,H-NBR, ACM, AEM, FKM, EPDM and the like.

As an alternative form of the cylindrical encoder, it may be obtained inthe following steps. The preliminary foundation processing may beconducted on the magnetic metal-based cylindrical body, an adhesivemedium may be applied onto the thus foundation processed cylindricalbody, and the rubber material containing the magnetic materialsmentioned above may be bonded to the cylindrical body by thevulcanizing, molding and bonding process. Finally, the cylindricalencoder thus obtained may be magnetized as described above.

Desirably, the metal-based body having the cylindrical shape around onwhich the magnetic rubber-based encoder having the cylindrical shape isformed may be made from magnetic material because the magnetic forcethat may be provided by the magnetic rubber-based encoder formed aroundthe outer peripheral surface of the cylindrical body can besupplemented.

In the cylindrical cover-attached encoder apparatus described above inaccordance with the present invention, the magnetic metal-basedcylindrical body should preferably be formed by using any of thesintered metals. The sintered metal can be worked into any desiredshape, and this can be done with the high dimensional precision.Specifically, the inner and outer peripheral surfaces of the sinteredmetal-based cylindrical body can be formed with the drastically enhanceddimensional precision. In short, the sintered metal can meet both thehigh precision magnetizing requirements and the mechanical strengthrequirements, and the cylindrical body can be secured in position withthe high stability.

In the cylindrical cover-attached encoder apparatus described above inaccordance with the present invention, the magnetic metal-basedcylindrical body may also be formed by using any of the steels.

In cases where the magnetic metal-based cylindrical body must be formedwith reduced thickness, it is preferable to form the magneticmetal-based cylindrical body by using a steal material. In those cases,the cylindrical cover-attached encoder apparatus that includes thecylindrical body based on the steel material can ensure the requiredmechanical strength. For example, the magnetic metal-based cylindricalbody may be formed by using low carbon steel such as SPCC, SPCE and thelike or ferrite stainless steel such as SUS430, SUS430JIL and the like.

In any of the before described cylindrical cover-attached encoderapparatus of the present invention, one end of the cylindrical portionof the nonmagnetic material-based cover covering the outer peripheralside of the encoder in the encoder apparatus may be extended beyond thecylindrical portion of the encoder in the axial direction of themagnetic metal-based cylindrical body, and the cover may then beattached to the encoder by swaging the one end of the cylindricalportion of the cover extending beyond the cylindrical portion of theencoder axially.

This swaging operation ensures that the nonmagnetic material-based covercan be attached to the encoder in the simplified way so that the covercan cover the encoder from the outside. This also ensures that the coverand encoder can be positioned relative to each other correctly andsecurely without being misaligned.

In any of the before described cylindrical cover-attached encoderapparatus of the present invention, it is desirable that the nonmagneticmaterial-based cylindrical cover has the thickness of between 0.1 mm and0.6 mm. In this way, the transmission of the magnetic force from theencoder through the cover can be improved, and the cover can be attachedto the encoder correctly and easily by the swaging operation.

In order to permit the nonmagnetic material-based cover to meet therequirements for the performance and mechanical strength, it may beformed by using SUS304, Al, CuZn, Cu and the like.

In the cylindrical cover-attached encoder apparatus of the presentinvention, the magnetic rubber-based cylindrical encoder may be formedaround the outer peripheral surface of the cylindrical portion of themagnetic metal-based cylindrical body, and thus the mechanical strengthof the encoder apparatus can be increased so remarkably that any damagesthat would otherwise occur when the encoder apparatus is pressed into aparticular rotational member on the automotive vehicle can be avoided.

The outer peripheral side of the magnetic rubber-based cylindricalencoder may be covered by the nonmagnetic material-based cover, and thusthe encoder can be protected more securely from the outside.

So that, the cylindrical cover-attached encoder can withstand the moresevere or vigorous running or ambient conditions for an extended periodof the time without causing any damages, even when it is used under suchconditions.

In accordance with any forms of the cylindrical cover-attached encoderapparatus of the present invention, the magnetic rubber-based encodercan be protected completely from the risk of any of the stones, sands,mud, dirty water and the like coming from the outside and hitting theencoder in the encoder apparatus, and any wear or breakage that would becaused by those stones, etc. can be avoided. Thus, the encoder in theencoder apparatus can be operating properly even under unfavorableenvironmental conditions almost permanently, and can provide pulses thatrepresent the number of revolutions accurately. Thus, those pulses fromthe encoder can be transmitted through the nonmagnetic material-basedcover, and can be detected accurately by the sensor.

It may be understood from the foregoing description that one end of thecylindrical portion of the nonmagnetic material-based cover covering theouter peripheral side of the encoder is extending beyond the cylindricalportion of the encoder in the axial direction of the magneticmetal-based cylindrical body. And, the cover may be attached to theencoder simply by swaging the one end of the cylindrical portion of thecover extending axially beyond the cylindrical portion of the encoder,thereby the nonmagnetic material-based cover can cover the encoder fromoutside it. This swaging operation can be carried out to ensure that thecover can be positioned correctly relative to the encoder without beingmisaligned.

It may be appreciated from the foregoing description that thecylindrical cover-attached encoder apparatus of the present inventionmay be used with the FF vehicle, for example, although it may also beused with other types of vehicles such as FR (front engine, rear drive)vehicle and RR (rear engine, rear drive) vehicle. In any case, theencoder apparatus can be mounted on the drive shaft, in which themagnetic rubber-based encoder can have its magnetized surface protectedby the nonmagnetic material-based cover, and can withstand any severe orvigorous running or environmental conditions for an extended period ofthe time, even when it is used under such conditions. Despite suchunfavorable situation, the encoder in the encoder apparatus of thepresent invention can produce pulses that represent the number ofrevolutions correctly, and the sensor can detect the number ofrevolutions accordingly by responding to the pulses.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(a) is a longitudinal sectional view of a preferred embodiment ofthe cylindrical cover-attached encoder apparatus according to thepresent invention, although some non-critical parts or elements are notshown, and FIG. 1(b) is a plan view of the cylindrical cover-attachedencoder apparatus shown in FIG. 1(a);

FIG. 2 is a longitudinal sectional view of another preferred embodimentof the cylindrical cover-attached encoder apparatus according to thepresent invention, showing how the encoder apparatus of FIG. 1 may bemounted on a rotational member in the automotive vehicle, although somenon-critical parts or elements are not shown; and

FIG. 3 is a longitudinal sectional view of still another preferredembodiment of the cylindrical cover-attached encoder apparatus, showinghow the encoder apparatus may be mounted on a rotational member in theautomotive vehicle, although some non-critical parts or elements are notshown.

DETAILS OF THE PREFERRED EMBODIMENTS

The following describes several particular preferred embodiments of thecylindrical cover-attached encoder apparatus according to the presentinvention by referring to the accompanying drawings.

Embodiments 1

The cylindrical cover-attached encoder apparatus according to the firstembodiment of the present invention includes the components that will bedescribed specifically below.

As one component of the encoder apparatus, a magnetic metal-basedcylindrical body 1 may be formed by using a sintered metal of magneticmaterials.

As another component of the encoder apparatus, an encoder may be formedin the following steps. A ferrite magnetic powder (such as strontiumferrite powder, barium ferrite powder and the like) and a rubberchemical are prepared, and may be added to NBR (acrylonitrile butadienerubber). Note that the strontium ferrite powder has the compositionratio of 88% by weight relative to the other elements. Then, they may bemixed together, and a rubber in its unvulcanized state may thus beobtained. Finally, this rubber is placed in a mold where it may bevulcanized, shaped into an encoder 2, and bonded to the outer peripheralsurface of the cylindrical body 1, as shown in FIG. 1(a).

In this embodiment, as shown in FIG. 1(a), the encoder 2 may be formedto have a cylindrical portion 2 b and annular portions 2 a, 2 a, inwhich the cylindrical portion 2 b may be bonded to the outer peripheralsurface of the cylindrical portion of the cylindrical body 1 and theannular portions 2 a, 2 a may be bonded to the upper lateral surface andlower lateral surface of the cylindrical body 1, respectively, duringthe vulcanizing, molding and bonding process.

Then, the cylindrical portion 2 b of the encoder 2 thus obtained may bemagnetized to have S polarities and N polarities appear alternately atequal intervals in the circumferential direction. Thus, the multipoleencoder 2 may be obtained. In this way, this multipole encoder 2includes the magnetic rubber that is formed around the outer peripheralsurface of the cylindrical portion of the magnetic metal-basedcylindrical body 1.

As still another component of the encoder apparatus, a cylindrical cover3 may be provided by using SUS304 steel plate of 0.3 mm thickness, forexample. As it may be seen from FIG. 1(a), the cylindrical cover 3 hasan annular portion 3 a.

This cylindrical cover 3 may be mounted to the outer peripheral side ofthe cylindrical encoder 2 formed around the outer peripheral surface ofthe cylindrical portion of the cylindrical body 1, this mounting beingmade in the direction of an arrow 5 in FIG. 1(a).

As it may be seen from FIG. 1(a), the cylindrical cover 3 has an end 3 cextending beyond the cylindrical portion 2b of the encoder 2 in theaxial direction of the magnetic metal-based cylindrical body 1.

The cylindrical. cover-attached encoder apparatus may be completed byswaging the end 3 c of the cylindrical cover 3 toward the direction ofan arrow 4, thereby attaching the cover 3 to the encoder 2.

In this embodiment, as shown in FIG. 1(a), the cylindrical encoder 2based on the magnetic rubber may be formed around the outer peripheralsurface of the cylindrical body 1, and the cylindrical cover 3 may thenbe mounted around the outer peripheral side of the cylindrical portion 2b of the cylindrical encoder 2, so that the inner peripheral wall of thecover 3 can engage the outer peripheral side of the cylindrical encoder2, and finally the cover 3 may be attached to the encoder 2 by swagingthe end 3 c of the cover 3. The cylindrical body 1, the cylindricalencoder 2 and the cylindrical cover 3 are thus combined together into asingle unit, thus completing the cylindrical cover-attached encoderapparatus of the present invention. Specifically, the cylindricalcover-attached encoder apparatus includes the cylindrical encoder 2, themagnetic metal-based cylindrical body 1, and the nonmagneticmaterial-based cylindrical cover 3 in such a way that the cylindricalencoder 2 is held like a sandwich between the magnetic metal-basedcylindrical body 1 and the nonmagnetic material-based cylindrical cover3.

Therefore, in the cylindrical cover-attached encoder apparatus of thepresent invention of this embodiment 1, the cylindrical encoder 2 madeof magnetic rubber is strengthen by the cylindrical body 1 made ofmagnetic metal, and the outer peripheral side of the cylindrical encoder2 made of magnetic rubber is covered by the cylindrical cover 3 made ofnonmagnetic material.

So that, in terms of the mechanical strength, the encoder 2 can bereinforced by the cylindrical body 1. Furthermore, the encoder 2 can beprotected by the nonmagnetic metal-based cylindrical cover 3 from theoutside. This permits the encoder apparatus to be positioned correctlywhen it is mounted on any rotational member on the automotive vehicle.Also, when it is used in conjunction with the sensor, the encoder 2 canprovide the number of revolutions correctly, which can be detected bythe sensor accordingly.

Now, the following describes how the encoder apparatus according to thisembodiment can be used. In the following description, it is supposedthat the encoder apparatus is used with FF (front engine, front drive)automotive vehicle. Then, the encoder apparatus may be mounted on aparticular rotational member, such as a drive shaft 7, by pressing theencoder apparatus into the drive shaft 7 in the direction of an arrow 9in FIG. 2. With the encoder apparatus being mounted on the drive shaft 7as shown in FIG. 2, the sensor 10 may be placed adjacently to the outerperipheral side of the cylindrical portion 3 b of the cover 3. Thisensures that the encoder 2 and sensor 10 can be operational for anextended period of the time so that the sensor 10 can detect the numberof revolutions by responding to the pulses emitted from the encoder 2mounted on the outer periphery of the drive shaft 7 rotating about therotary axis 8.

Embodiments 2

In this embodiment, it is assumed that the cylindrical cover-attachedencoder apparatus may be mounted on a rotational member, such as abearing unit including the inner and outer races rotating relative toeach other through the rolls interposed between the inner and outerraces. As shown in FIG. 3, a cylindrical core metal is provided so thatit can be mounted on the outer periphery of the outer race of thebearing unit, and an encoder is provided so that it can be formed on theouter periphery of the core metal. A nonmagnetic material-basedcylindrical cover is provided so that it can be attached to the outerperipheral side of the encoder by using the swaging process.

It may be seen from FIG. 3 that the encoder apparatus is mounted on thewheel bearing unit on the driven shaft, including the inner race 16 aand outer race 16 b rotating relative to each other though theintervening rolls 17.

As a component of the encoder apparatus, a cylindrical core metal 11 maybe provided by using a low carbon steel such as SPCC. The cylindricalcore metal 11 may be formed to include a cylindrical portion 11 b and aflange portion 11 a. The cylindrical portion 11 b is placed on the outerperiphery of the rotating outer race 16 b of the wheel bearing unit. Theflange portion 11 a is extending inwardly (the left side in FIG. 3) inthe radial direction from the axial outer end (the upper side in FIG. 3)of the cylindrical portion 11 b.

Then, the preliminary foundation processing may be conducted on theouter peripheral surface of the cylindrical core metal 11, onto which anadhesive medium may be applied.

As another component of the encoder apparatus, a cylindrical encoder maybe formed in the following steps. A ferrite magnetic powder (such as amixture of strontium ferrite powder and barium ferrite powder) and arubber chemical are prepared, and may be added to H-NBR (hydrogen-addedacrylonitrile butadiene rubber). Note that the ferrite magnetic powderhas the composition ratio of 88% by weight relative to the otherelements. Then, they may be mixed together, and a rubber in itsunvulcanized state may thus be obtained. Finally, this rubber is placedin a mold where it may be vulcanized, shaped into the magneticrubber-based cylindrical encoder 13, and bonded on the outer peripheralsurface of the cylindrical core 11.

In this embodiment, as shown in FIG. 3, the magnetic rubber-basedcylindrical encoder 13 includes a cylindrical portion 13 b and anannular portion 13a, and the vulcanizing, molding and bonding processmay be carried out on the cylindrical encoder 13 with its cylindricalportion 13 b being bonded to the outer peripheral side of thecylindrical portion 11 b of the core metal 11 and the annular portion 13a being bonded to the flange portion 11 a of the metal core 11.

Then, the magnetic rubber-based cylindrical encoder 13 may be magnetizedso that S polarities and N polarities can appear alternately at equalintervals in the circumferential direction of the cylindrical portion 13b, and may be provided on the outer peripheral surface of thecylindrical portion 11 b of the SPCC steel-based cylindrical core metal11.

As still another component of the encoder apparatus, a cylindrical cover14 may be provided by using a SUS304 steel plate of 0.3 mm thickness,including a cylindrical portion 14 b and a flange portion 14 a extendinginwardly (the left side in FIG. 3) in the radial direction from theaxial outer end (the upper end in FIG. 3) of the cylindrical portion 14b.

Then, the SUS304 steel-based cylindrical cover 14 may be mounted on theouter peripheral side of the cylindrical encoder 13 formed on the outerperiphery of the cylindrical portion 11 b of the cylindrical core metal11, in the same manner as described for the preceding embodiment 1.

The cylindrical cover 14 has an end 14 c extending beyond thecylindrical portion 13 b of the encoder 13 in the axial direction of thecylindrical portion 11 b of the core metal 11, and may be attached tothe encoder 13 by swaging the end 14 c in the direction of an arrow 15.The cylindrical cover-attached encoder apparatus is thus completed.

Similarly to the preceding embodiment 1, the cylindrical magneticrubber-based encoder 13 is firmly held like a sandwich as shown in FIG.3. Therefore, in the cylindrical cover-attached encoder apparatus of thepresent invention, the cylindrical encoder 13 made of magnetic rubber isstrengthen by the core metal 11 made of magnetic metal, and the outerperipheral side of the cylindrical encoder 13 made of magnetic rubber iscovered by the cylindrical cover 14 made of nonmagnetic material. Sothat, in terms of the mechanical strength, the encoder 13 can bereinforced by the core metal 11. Furthermore, the encoder 13 can beprotected by the nonmagnetic metal-based cylindrical cover 14 from theoutside. This permits the encoder apparatus to be positioned correctlywhen it is mounted on any rotational member on the automotive vehicle.Also, when it is used in conjunction with the sensor, the encoder 13 canprovide the number of revolutions correctly, which can be detected bythe sensor accordingly.

The cylindrical cover-attached encoder apparatus thus obtained inaccordance with this embodiment may be mounted on a particularrotational member in the automotive vehicle, such as the outer race 16 bof the wheel bearing unit on the driven shaft. With the encoderapparatus being mounted on the outer race 16 b as shown in FIG. 3, thesensor 10 may be placed adjacently to the outer peripheral side of thecylindrical portion of the cover 14. This ensures that the encoder 13and sensor 10 can be operational for an extended period of the time sothat the sensor 10 can detect the number of revolutions by responding tothe pulses emitted from the encoder 13 mounted on the outer periphery ofthe outer race 16 b of the rotating bearing unit.

Although the present invention has been described so far with referenceto several particular preferred embodiments thereof, it should beunderstood that various changes and modifications may be made to thoseembodiments without departing from the spirit and scope of the inventionas defined in the appended claims.

1. A cylindrical cover-attached encoder apparatus, including: a magneticmetal-based body having a cylindrical shape; a magnetic rubber-basedencoder having a cylindrical shape and formed around the outerperipheral surface of said magnetic metal-based cylindrical body; and anonmagnetic material-based cover having a cylindrical shape and adaptedto be mounted on said magnetic rubber-based encoder for covering theouter peripheral surface of the cylindrical portion of said magneticrubber-based encoder.
 2. The cylindrical cover-attached encoderapparatus as defined in claim 1, wherein the magnetic metal-basedcylindrical body is formed by using any of the sintered metals.
 3. Thecylindrical cover-attached encoder apparatus as defined in claim 1,wherein the magnetic metal-based cylindrical body is formed by using anyof the steel materials.
 4. The cylindrical cover-attached encoderapparatus as defined in claim 1, wherein one end of the cylindricalportion of said nonmagnetic material-based cover which covers the outerperipheral surface of the magnetic rubber-based encoder is extendingbeyond the cylindrical portion of the magnetic rubber-based encoder inthe axial direction of the magnetic metal-based cylindrical body andwherein the nonmagnetic material-based cover is attached to the magneticrubber-based encoder by swaging the one end of the cover which extendingbeyond the cylindrical portion of the magnetic rubber-based encoder. 5.The cylindrical cover-attached encoder apparatus as defined in claim 2,wherein one end of the cylindrical portion of said nonmagneticmaterial-based cover which covers the outer peripheral surface of themagnetic rubber-based encoder is extending beyond the cylindricalportion of the magnetic rubber-based encoder in the axial direction ofthe magnetic metal-based cylindrical body and wherein the nonmagneticmaterial-based cover is attached to the magnetic rubber-based encoder byswaging the one end of the cover which extending beyond the cylindricalportion of the magnetic rubber-based encoder.
 6. The cylindricalcover-attached encoder apparatus as defined in claim 3, wherein one endof the cylindrical portion of said nonmagnetic material-based coverwhich covers the outer peripheral surface of the magnetic rubber-basedencoder is extending beyond the cylindrical portion of the magneticrubber-based encoder in the axial direction of the magnetic metal-basedcylindrical body and wherein the nonmagnetic material-based cover isattached to the magnetic rubber-based encoder by swaging the one end ofthe cover which extending beyond the cylindrical portion of the magneticrubber-based encoder.